If hiruzen was in cave instead of that loser , I mean kabuto then both sasuke and itachi Will definitely lose and they will be sent to their crave ..
i will explain why he can take both sasuke and itachi at same time:
1) hiruzen is strongest hokage (manga fact)
2) hiruzen soloed both hashirama and Tobirama in 1shot (manga fact)
3) hiruzen knows every konoha jutsu including uchiha jutsu that doesn't require eyes like sasunoo and amatarsu.
4) hiruzen knows FTG , he arrived at same time as Tobirama in battlefield.
5) hiruzen age was 69 when he died , his power in databook is 35/40 which mean in his prime his power was 40/40
6) hiruzen have higher experience than itachi and sasuke so he can 1shot them.
Finally itachi himself feared from hiruzen and that's manga fact too ..
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